It is a problem to remove heat from systems using densely packed, high-power devices. Many prior art systems use convection cooling to remove heat. To work efficiently, systems cooled by convection currents require means, such as fans or pumps, to move large amounts of a cooling fluid across the heat generating devices. This makes convection cooling inappropriate for compact low-profile portable computer systems equipped with high-speed CPU chips.
In compact systems, heat sinks are typically connected to the heat generating devices so that the heat can be conducted, instead of convected away. Frequently it is desired to construct the system so that the heat sink and the heat generating device can be decoupled. This makes servicing, repairing, and replacing of the heat generating devices easy.
In addition, it also desired to reduce stress at the thermal connection. The stress can be caused by differences in thermal expansion rates of the heat generating and removal components and by mechanical shock and vibration. Furthermore, in order to construct slim portable systems, the total vertical height of component assemblies must be maintained at a minimum.
In the prior art, interleaved-fin thermal connectors have been used to provide a thermal conductive path between the heat generating device and the heat removal mechanism. For example, U.S. Pat. No. 4,800,956, "Apparatus and Method for Removal of Heat from Packaged Element", and U.S. Pat. No. 5,083,373 "Method for Providing a Thermal Transfer Device for the Removal of Heat from Packaged Elements" describe thermal transfer assemblies including two sets of cooling fins. The fins can be interleaved with each other to provide a detachable thermal connection.
There are several problems with these prior art thermal connectors. First, the assembly of the elements requires several steps which do not readily admit automation. For example, the fabrication of the prior art interleaved devices requires a tape material to hold the fins in place during assembly. For example, the tape is intertwined between the fins. Next, the fins can be forced against a base plate by a jig. While held in this position, the fins can be joined to the base plate using solder. Once the fins are fixed to the base, the tape can be removed.
Second, the prior art fins and bases are made of heat conducting metals, for example, copper or specially prepared aluminum. These metals are well suited for fabrication and soldering of large scale components. However, it would be extremely difficult to make copper or prepared aluminum fins having a vertical height in the range of millimeters or less, and widths measured in terms of microns.
Even if rigid small fins and bases could be constructed, connecting the metallic fins and bases would be extremely difficult using the jigged tape and soldering methods described above. Such methods are not suited for low-cost mass production techniques.
Third, there may be differences between thermal expansion rates of the semiconductor devices and the fins and bases of the prior art assemblies. These differences would stress the joint where the assemblies are attached, leading to possible failures.
Therefore, it is desired to provide a detachable thermally conductive path from the heat source directly to the heat sink. Furthermore, the path should have a small vertical dimension. In addition, it is desired that the thermal path has freedom of movement in a maximum number of different directions.